Electrical over/under voltage automatic disconnect apparatus and method

ABSTRACT

An analog or digital circuit that senses both low and high input voltage and operates to disconnect both line and neutral electrical power connections to a protected device when abnormally low or high voltages are received from a single- or multi-phase power source, and reconnects the protected device when input power has stabilized. The sensing circuit and power supply is functional with voltages up to at least 240 Vac. The nominal 120 Vac circuit is designed to withstand a 6 kilovolt surge without damage. The apparatus does not disconnect the ground line during an out-of-tolerance voltage condition.

TECHNICAL FIELD

[0001] An apparatus to automatically disconnect both hot line (L) andneutral (N) connections, but not the ground (G) connection, to a powercenter whenever the continuous voltage between any two wires (L-N, L-G,N-G) exceed a pre-determined voltage of alternating current andautomatically reconnects the outlet power center when the voltagereturns to an acceptable level. The apparatus may use either analog ordigital logic and is applicable to single or multiphase power sources upto 250 volts (Vac) or more. The apparatus further senses the suppliedvoltage and prevents a connection of the load to the power source if thesupplied voltage is less than a pre-determined level.

BACKGROUND ART

[0002] It is common in the electrical art to use surge protectivedevices in the power supply of electronic equipment See, for example,U.S. Pat. No. 5,978,198 to Packard et al. Metal oxide varistors (MOVs)are frequently used to provide surge protection. MOVs are designed toabsorb an enormous amount of power for a very short time, such as occursduring a power line surge condition. However, MOVs can easily bedamaged, with serious consequences, if the line voltage exceeds the saferatings (typically 275 V) for the MOVs for more than a short period,commonly approximately 100 milliseconds (ms). What is needed is acircuit that will detect unsafe voltages or currents and disconnect thepower through the MOV system when the voltage exceeds the safe limit andbefore the MOVs or other components are damaged, and reconnect it whenthe voltage returns to and stabilizes in a safe range. What is furtherneeded is a circuit that will sense an out-of-tolerance low voltage anddisconnect the power through the MOV system when such low voltageconditions exist and automatically reconnect it when the voltage returnsto and stabilizes in a safe range.

[0003] Another common problem in the electrical art is mis-wiring of theelectrical source, such as errors made in connecting the commonhousehold electrical outlet. While common household outlets areconfigured to accept the three wires, L, N, and G, there is no physicalbarrier in common household electrical outlets that prevents the wiresbeing connected to the wrong terminals. See, for example, U.S. Pat. No.6,040,969 to Winch et al. for an apparatus to address this problem. Whatis needed is a surge protection device that can also detect incorrectwiring, in addition to out-of-tolerance voltages, and prevent conductionof electrical power through to a device to be protected.

DISCLOSURE OF INVENTION

[0004] The following discussion of the present invention is presented interms of a single phase, nominal 120 Vac circuit for simplicity ofunderstanding the invention. The present invention is also applicable tomulti-phase circuits and voltages up to nominal 240 Vac. Higher voltagesmay be possible, depending on the availability of components withsuitable tolerances. The invention is applicable to surge protectiondevices and the like used to protect sensitive electronic devices havingmicrocircuit components, such as computers, audio and visual equipment,from dangerous conditions such as out of specification voltages andcurrent surges. The invention includes a circuit that senses both lowand high input voltage and activates at least one relay to disconnectboth line and neutral electrical power connections to a protecteddevice, before the apparatus suffers electrical damage such as a blownmetal oxide varistor or fuse, when abnormally low or high voltages arereceived from a power source. The sensing circuit and power supply for anominal 120 Vac single phase circuit is able to withstand a continuous250 Vrms (volts, root-mean-square) or more for more that 100milliseconds (ms). The circuit is further designed to withstand a 6kilovolt (kV) surge without damage. Power surges are also detected andabsorbed. The apparatus does not disconnect the ground (G) line duringan out-of-tolerance voltage condition. The invention continues tomonitor the input power source and automatically reconnects the loadwhen the source has demonstrated acceptable voltages for a set period oftime, typically 10 to 20 seconds, and preferably 15 seconds. The analogand digital exemplary embodiments described below provide surgeprotection meeting the Underwriter's Laboratory 1449 standard, includinga 6 kV 8×20 microsecond @ 3000 ampere surge test under L-N, L-G and N-Gmis-wiring scenarios, without component damage.

BRIEF DESCRIPTION OF THE DRAWING

[0005] The invention will be more fully understood by reference to thefollowing drawing which is for illustrative purposes only and where likereference numbers denote like elements.

[0006]FIG. 1 is a block diagram of an exemplary apparatus according tothe present invention.

[0007]FIG. 2 is a logic diagram of a digital control circuit for anexemplary apparatus according to the present invention.

[0008]FIG. 3 is a schematic diagram of the exemplary analog apparatus ofFIG. 1.

[0009]FIG. 4 is a schematic diagram of the exemplary digital apparatusof FIG. 1.

MODES FOR CARRYING OUT THE INVENTION

[0010] The following discussion of the present invention is presented interms of a single phase, nominal 120 Vac circuit for simplicity ofunderstanding the invention. The present invention is also applicable tomulti-phase circuits and voltages up to nominal 240 Vac. Higher voltagesmay be possible, depending on the availability of components withsuitable tolerances. The present invention is an apparatus containing anelectrical analog circuit that provides automatic disconnect protectionto any electrical device connected with the apparatus. Both analog anddigital control circuits are contemplated by the present invention. Theapparatus comprises a cord having a plug 1 for connecting to a source ofalternating current (AC) power, such as an ordinary household electricaloutlet. Alternatively, the apparatus could be hard wired into another,larger device, such as an equipment rack or another electrical device.The apparatus may contain individual outlets 5 for receiving the plugsof electronic devices to be so protected, or alternatively, theprotected devices may be other electronic components hard wired to theapparatus of the present invention.

[0011] The following description of the exemplary analog and digitalembodiments is in terms of a nominal 120 Vac power source. Alternativeembodiments suitable for other power sources or higher voltages, usingappropriately-sized components, will be readily apparent to apractitioner skilled in the electrical arts and are herein included byreference.

[0012] Referring to FIG. 1, a block diagram of an exemplary embodimentof the present invention is shown. Electrical over/under voltagedisconnect apparatus 100 is a disconnect circuit unit 10 having powerinput connector 1 and power output connector 5. Connector 1 is a threewire connection having line 2, neutral 3 and ground 4 components.Connector 1 may be either a three-wire cable having a three-prong plugfor plugging into an ordinary ac power outlet of approximately either120 Vrms or 250 Vrms, or may alternatively be wire connections madedirectly to the line, neutral and ground of the power source(hard-wired). Output connector 5 may be either a three-prong receptaclesuitable for receiving a plug from an electrical device to be protected,or may alternatively be hard wired as line 2, neutral 3 and ground 4directly to an electrical device to be protected. Output connector 5 mayalso be a multiple outlet device for receiving the power plugs of morethan one device, i.e., a multitap device.

[0013] Unit 10 is an electrical circuit having relays K1 and K2 fordisconnecting line 2 and neutral 3 respectively when commanded to do soby voltage sensing and control circuit 11. Relays K1 and K2 arepreferably individual normally open single pole relays but may be asingle double pole normally open relay. Normally open relays K1 and K2connect line 2 and neutral 3 respectively when the voltage of thesupplied power is below approximately 132 Vrms and above approximately60 Vrms and control circuit 11 routes power to relays K1 and K2. Controlcircuit 11 may be of either analog or digital form. When control circuit11 senses voltages in excess of the designed maximum or less than thedesigned minimum, control circuit 11 reroutes the electrical power fromrelays K1 and K2, thereby opening line 2 and neutral 3 and protectingany device connected to connector 5. Control circuit 11 continues tomonitor the input power voltage and will reconnect connector 5 byreclosing relays K1 and K2 when the out-of-tolerance voltage conditionis no longer present and has remained so for approximately 10 to 20seconds. In the exemplary embodiment, the disconnect time isapproximately less than 100 milliseconds and -is determined by thereaction time of relays K1 and K2. Additionally, the maximumdisconnect/reconnect current is approximately 15 amperes, againdepending on the performance capacity of relays K1 and K2. In theexemplary example, unit 10 is able to withstand continuous 300 Vrmsbetween line 2-neutral 3, line 2-ground 4, or neutral 3-ground 4 withoutcomponent damage.

[0014] Referring to FIG. 2, a logic diagram of a digital control circuit11 of exemplary apparatus 100 according to the present invention isshown. Block 20 represents determining the presence of at least minimumspecification voltages immediately upon application of power to circuit11. Block 21 represents lighting of an light emitting diode to indicatepower-up status. Block 22 represents the first analog electricalsampling of the input power, line 2, neutral 3 and ground 4. Block 23represents the initial determination of the power quality. If power isnot within specification, the logic returns to block 21; if it is withinspecification, the logic proceeds to block 24. The stabilization periodrepresented by block 24 is determined by the microcontroller and istypically 100 to 200 ms. Block 25 represents a second determination ofpower quality, with out -of-specification power resulting in a return toblock 21 and within-specification power resulting in progression toblock 26. Block 26 represents the updating of the status LEDs andactivation of relays K1 and K2. Blocks 27-30 represent the continualmonitoring of power quality, with block 31 representing the action takenif the power quality strays out of specification for the time delayperiod, block 29. Block 29 time delay is typically one cycle of the 60hertz powerline wave form, or 16 ms.

[0015] Referring now to FIG. 3, a schematic diagram of the exemplaryanalog embodiment circuit unit 100 is shown. Table 1 identifies thecomponents of FIG. 3. TABLE 1 TABLE 1 ANALOG EMBODIMENT COMPONENTLISTING Reference Quantity Part C1 1 0.0047 μf/1000 v C2, C4 2 220 μf/63v C3 1 47 μf/450 v C5 1 22 μf/25 v D1, D2, D5, 5 1N4007 D6, D8 D9, D11,3 1N4007 D12 D3, D16 2 1N4007 D7, D17 2 15 v/1 w D10 1 Green LED D13 1Red LED D14, D15 2 1N4148 F1 1 250 ma J1-J6 6 CON1 K1, K2 2 48 v COIL,30 a 250 v 15 a 125 v CONTACT, OMRON G8P-1114P-US MOV1 1 450 v varistorQ1-Q4 4 MPSA44 R1, R16 2 4 M ½ W R2 1 12K R3, R6, R19 3 100K R4, R17, 347K R18, R19-R21 3 47K R5 1 1K/25 W R7, R11, 3 120K R13 R8 1 220K ½ W R91 100K 1 W R10 1 11K 20 W R12 1 560K R14 1 20K R15 1 4M R20, R22 2 5KR21 1 240K U1, U2 2 LM393A U3 1 4N35

[0016] TABLE 2 DIGITAL EMBODIMENT COMPONENT LIST C1 1 0.0221 μF/250 V C21 50 μF/50 V C3 1 10 μF/25 V D1-D5, D7, D10, D12, D14-D16 11 1N4007diodes D6 1 15 V, 1 Watt zener diode D8-9, D11, D13 4 5.1 V, 1 Wattzener diodes K1, K2 2 48 V coil, (30 A 250 V 15 A 125 V contact) OMRONG8P-1114P-UA or similar L1 1 56 μH, 1.48 A Q1, Q2 2 4401 NPN transistorR1-R4 4 2.2K, 1 Watt R5-R6 2 1.5K, 1 Watt R7-R12 6 1.3M, ½ Watt R13-R16,R18-R19 6 20K, ½ Watt R17, R20 2 10K R21-R22 2 4.7K U1 1 7805 + 5 Vregulator U2 1 P1C1212CE674, or similar 4 channel analog- to-digitalmicrocontroller

[0017] In the exemplary embodiment, relays K1 and K2 are normally openwhen not energized. Under normal voltage conditions these relays will beenergized, allowing line 2 and neutral 3 to conduct from input connector1 to output connector 5. Full wave bridge rectifier diodes D8, D9, D10and D12 rectify a portion of the received AC power to non-filteredfull-wave waveform to be monitored by comparators U1A and U2A for overvoltage. The voltage is routed, reduced, filtered and regulated to 15Vdc by zener diodes D7 and D17 and R10, C2 and C4 to power thecomparators. The comparator U2A monitors L-N and positive G-L, Nvoltage. R11 and R20 on U2A set the reference voltage with respect topin 4 of U2A. When L-N or positive G-L, N instantaneous voltage exceeds132 Vrms, scaled down voltage at U2A pin 2 will be higher than pin 3.The transistor in U2A at pin 1 will conduct and discharge capacitor C5,making pin 7 of U2B go low. When the voltage at pin 7 of U2B goes low,the current through R14 that is normally used to turn on the relays isrouted instead to U2B. The relays K1 and K2 will be de-energized anddisconnect the line and neutral circuits instantaneously. When linevoltage returns to normal, the R12 and C15 combination delays therelays' reconnect time by 15 seconds.

[0018] The comparator U1A does the same thing as U2A but on negativeG-L, N over voltage. Opto isolator U3 sends this over voltage signal toU2B. Transistors Q1 and Q3 cut off voltage to filter capacitor C3 duringthe over voltage condition. This will prevent relays K1 and K2 coilbreakdown from voltage stored in the capacitor during high voltageconditions, when reconnecting the line.

[0019] In the digital embodiment, the functions of control circuit 11are performed by a microprocessor instead of the analog componentsdescribed above. Microprocessor logic is shown in FIG. 2 and anexemplary schematic is shown in FIG. 4. The components are listed inTable 2. A preferred microcontroller having EEPROM capability isavailable from Microchip, as model PIC12C672 or model PIC12C674(www.microchip.com). The preferred microcontroller has at least threeanalog-to-digital (ADC) input pins for sensing all the voltage mains(Line, Neutral, Ground). The microcontroller is a 4 MHz, or greater,processor which will sample all three mains in 1 ms or less. It takesmultiple samples, at least 10 times or more, of the mains' voltage,scaled down using high tolerance resistors, for appropriate sampleaveraging. Other, similar, microcontrollers are also available and maybe substituted as long as they have the appropriate characteristics.

[0020] The analog and digital apparatuses protect for three mis-wiringscenarios. The exemplary apparatus functions to detect and protectagainst three common mis-wiring scenarios in which the input powervaries from that normally expected, i.e., the normal is where the line 2is +120 Vac, the neutral 3 is 0 Vac and the ground is properly connectedto an earthen ground. Mis-wiring scenario A has line 2 connected to +120Vac, neutral 3 connected to neutral, and ground 4 connected to −120 Vac.Scenario B has line 2 connected to neutral, neutral 3 connected to −120Vac, and ground 4 connected to +120 Vac. Scenario C has line 2 connectedto - 120 Vac, neutral 3 connected to +120 Vac, and ground 4 connected toneutral.

[0021] Information as herein shown and described in detail is fullycapable of attaining the above-described object of the invention, thepresently preferred embodiments of the invention, and is, thus,representative of the subject matter which is broadly contemplated bythe present invention. The scope of the present invention fullyencompasses other embodiments which may become obvious to those skilledin the art, and is to be limited, accordingly, by nothing other than theappended claims, wherein reference to an element in the singular is notintended to mean “one and only one” unless explicitly so stated, butrather “one or more”. All structural, electrical, and functionalequivalents to the elements of the above-described preferred embodimentand additional embodiments that are known to those of ordinary skill inthe art are expressly incorporated herein by reference and are intendedto be encompassed by the present claims.

[0022] Moreover, it is not necessary for a device or method to addresseach and every problem sought to be solved by the present invention forit to be encompassed by the present claims. Furthermore, no element,component, or method step in the present disclosure is intended to bededicated to the public regardless of whether the element, component, ormethod step is explicitly recited in the claims. No claim element hereinis to be construed under the provisions of 35 U.S.C. 112, sixthparagraph, unless the element is expressly recited using the phrase“means for”.

INDUSTRIAL APPLICABILITY

[0023] The present invention may be used to protect electrically powereddevices such as audio, visual and digital apparatuses and the like fromdangerous electrical power surges, low and high voltages and othertransient forces that may be imposed on electrical power sources, forexample by lightning strikes or “brown-out” power conditions. Theinvention may be made by technicians familiar with electrical anddigital components available in the market place. The apparatus detectsan out-of-tolerance condition and disconnects a load from a powersource, then reconnects the load when the power source has been stableand within tolerance for a set period of time.

What is claimed is:
 1. An electrical apparatus comprising: connectingmeans for connecting the apparatus to a supply of at least one phase ofalternating current power having a line, neutral and ground; sensingmeans for sensing the voltage of the supplied power across theline-neutral, line-ground and neutral-ground; distribution means fordistributing the sensed power; and disconnecting means for disconnectingthe distribution means from the power source when the sensing meansdetects an out-of-tolerance voltage condition, wherein the sensing meansactivates the disconnecting means before the apparatus sufferselectrical damage.
 2. The apparatus in accordance with claim 1 whereinthe connecting means is a three-conductor electrical cord having athree-prong plug and the distribution means is at least one three-prongreceptacle
 3. The apparatus in accordance with claim 1 wherein thesensing means is selected from a group comprising analog circuitry,digital circuitry.
 4. The apparatus in accordance with claim 3 whereinthe sensing means can detect voltages in excess of 132 Vrms and voltagesof less that 60 Vrms.
 5. The apparatus in accordance with claim 1wherein the supply of alternating current power is a three phase source.6. The apparatus in accordance with claim 1 wherein the connecting meansis a relay having separate contacts for the line and neutral.
 7. Theapparatus in accordance with claim 1 wherein the out-of-tolerancevoltage condition is a voltage of less than approximately 60 Vrms orgreater than approximately 132 Vrms.
 8. The apparatus of claim 3 furtherhaving a reconnecting means for reconnecting the sensed power to thedistribution means when the sensing means no longer detects an out-oftolerance voltage condition.
 9. The apparatus of claim 8 wherein thereconnecting means has a delay of approximately 15 seconds when thesensing means no longer detects an out-of-tolerance voltage condition.10. An electrical apparatus comprising: connecting means for connectingthe apparatus to a supply of at least one phase of alternating currentpower having a line, neutral and ground; sensing means for sensing thevoltage of the supplied power across the line-neutral, line-ground andneutral-ground, wherein the sensing means can detect voltages in excessof 132 Vrms and voltages of less that 60 Vrms; distribution means fordistributing the sensed power; disconnecting means for disconnecting thedistribution means from the power source when the sensing means detectsan out-of-tolerance voltage condition, wherein the sensing meansactivates the disconnecting means before the apparatus sufferselectrical damage; and reconnecting means for reconnecting the sensedpower to the distribution means when the sensing means no longer detectsan out-of-tolerance voltage condition, wherein the reconnecting meanshas a delay of approximately 15 seconds when the sensing means no longerdetects an out-of-tolerance voltage condition.
 11. The apparatus ofclaim 10 wherein the sensing means is selected from a group comprisinganalog devices, digital devices.
 12. The apparatus in accordance withclaim 10 wherein the out-of-tolerance voltage condition is a voltage ofless than approximately 60 Vrms or greater than approximately 132 Vrms.13. A method of providing electrical over/under voltage protectioncomprising: providing a connecting means for connecting to a supply ofat least one phase of alternating current power having a line, neutraland ground; providing a sensing means for sensing the voltage of thesupplied power; providing a distribution means for distributing thesensed power; and providing a disconnecting means for disconnecting thedistribution means from the power source when the sensing means detectsan out-of-tolerance voltage condition across the line-neutral,line-ground or neutral-ground, wherein the sensing means activates thedisconnecting means before the apparatus suffers electrical damage. 14.The method in accordance with claim 13 wherein providing a sensing meanscomprises selecting a sensing means selected from a group comprisinganalog devices, digital devices.
 15. The method in accordance with claim14 wherein the sensing means detects voltages in excess of 132 Vrms. 16.The method in accordance with claim 14 wherein the sensing means detectsvoltages of less that 60 Vrms.
 17. The method in accordance with claim13 wherein the distribution means distributes power through at least onethree-prong electrical outlet receptacle.
 18. The method in accordancewith claim 13 wherein detection of the out-of-tolerance voltagecondition is detection of a voltage of less than approximately 60 Vrmsor greater than approximately 132 Vrms.
 19. The method of claim 13further comprising providing a reconnecting means for reconnecting thesensed power to the distribution means when the sensing means no longerdetects an out-of-tolerance voltage condition.
 20. The method of claim19 wherein the reconnecting means activates after a delay ofapproximately 15 seconds when the sensing means no longer detects anout-of-tolerance voltage condition.